I know of one second hand market by babaoshan called Babaoshan Secondhand Market 八宝山旧货市场 but it's quite a trek (near babaoshan subway). The place is more like a junk market and you'll find a bit of everything here. If you're lucky you may be able to find a decent piece of furniture among the junk.

There are a number of service providers are available in the both onsite as well as offsite market.. By utilizing the references of those people will help you to buy furnitures and you can also get a clear idea through http://worldoffurnitures.com/